/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.util.xml;

import javax.xml.namespace.QName;
import javax.xml.stream.Location;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.ext.Locator2;
import org.xml.sax.helpers.AttributesImpl;

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

/**
 * SAX {@code XMLReader} that reads from a StAX {@code XMLStreamReader}. Reads from an
 * {@code XMLStreamReader}, and calls the corresponding methods on the SAX callback interfaces.
 *
 * @author Arjen Poutsma
 * @see XMLStreamReader
 * @see #setContentHandler(org.xml.sax.ContentHandler)
 * @see #setDTDHandler(org.xml.sax.DTDHandler)
 * @see #setEntityResolver(org.xml.sax.EntityResolver)
 * @see #setErrorHandler(org.xml.sax.ErrorHandler)
 * @since 3.0
 */
class StaxStreamXMLReader extends AbstractStaxXMLReader {

    private static final String DEFAULT_XML_VERSION = "1.0";

    private final XMLStreamReader reader;

    private String xmlVersion = DEFAULT_XML_VERSION;

    @Nullable
    private String encoding;


    /**
     * Construct a new instance of the {@code StaxStreamXmlReader} that reads from the given
     * {@code XMLStreamReader}. The supplied stream reader must be in {@code XMLStreamConstants.START_DOCUMENT}
     * or {@code XMLStreamConstants.START_ELEMENT} state.
     *
     * @param reader the {@code XMLEventReader} to read from
     * @throws IllegalStateException if the reader is not at the start of a document or element
     */
    StaxStreamXMLReader(XMLStreamReader reader) {
        Assert.notNull(reader, "XMLStreamReader must not be null");
        int event = reader.getEventType();
        if (!(event == XMLStreamConstants.START_DOCUMENT || event == XMLStreamConstants.START_ELEMENT)) {
            throw new IllegalStateException("XMLEventReader not at start of document or element");
        }
        this.reader = reader;
    }


    @Override
    protected void parseInternal() throws SAXException, XMLStreamException {
        boolean documentStarted = false;
        boolean documentEnded = false;
        int elementDepth = 0;
        int eventType = this.reader.getEventType();
        while (true) {
            if (eventType != XMLStreamConstants.START_DOCUMENT && eventType != XMLStreamConstants.END_DOCUMENT &&
                    !documentStarted) {
                handleStartDocument();
                documentStarted = true;
            }
            switch (eventType) {
                case XMLStreamConstants.START_ELEMENT:
                    elementDepth++;
                    handleStartElement();
                    break;
                case XMLStreamConstants.END_ELEMENT:
                    elementDepth--;
                    if (elementDepth >= 0) {
                        handleEndElement();
                    }
                    break;
                case XMLStreamConstants.PROCESSING_INSTRUCTION:
                    handleProcessingInstruction();
                    break;
                case XMLStreamConstants.CHARACTERS:
                case XMLStreamConstants.SPACE:
                case XMLStreamConstants.CDATA:
                    handleCharacters();
                    break;
                case XMLStreamConstants.START_DOCUMENT:
                    handleStartDocument();
                    documentStarted = true;
                    break;
                case XMLStreamConstants.END_DOCUMENT:
                    handleEndDocument();
                    documentEnded = true;
                    break;
                case XMLStreamConstants.COMMENT:
                    handleComment();
                    break;
                case XMLStreamConstants.DTD:
                    handleDtd();
                    break;
                case XMLStreamConstants.ENTITY_REFERENCE:
                    handleEntityReference();
                    break;
            }
            if (this.reader.hasNext() && elementDepth >= 0) {
                eventType = this.reader.next();
            } else {
                break;
            }
        }
        if (!documentEnded) {
            handleEndDocument();
        }
    }

    private void handleStartDocument() throws SAXException {
        if (XMLStreamConstants.START_DOCUMENT == this.reader.getEventType()) {
            String xmlVersion = this.reader.getVersion();
            if (StringUtils.hasLength(xmlVersion)) {
                this.xmlVersion = xmlVersion;
            }
            this.encoding = this.reader.getCharacterEncodingScheme();
        }
        if (getContentHandler() != null) {
            final Location location = this.reader.getLocation();
            getContentHandler().setDocumentLocator(new Locator2() {
                @Override
                public int getColumnNumber() {
                    return (location != null ? location.getColumnNumber() : -1);
                }

                @Override
                public int getLineNumber() {
                    return (location != null ? location.getLineNumber() : -1);
                }

                @Override
                @Nullable
                public String getPublicId() {
                    return (location != null ? location.getPublicId() : null);
                }

                @Override
                @Nullable
                public String getSystemId() {
                    return (location != null ? location.getSystemId() : null);
                }

                @Override
                public String getXMLVersion() {
                    return xmlVersion;
                }

                @Override
                @Nullable
                public String getEncoding() {
                    return encoding;
                }
            });
            getContentHandler().startDocument();
            if (this.reader.standaloneSet()) {
                setStandalone(this.reader.isStandalone());
            }
        }
    }

    private void handleStartElement() throws SAXException {
        if (getContentHandler() != null) {
            QName qName = this.reader.getName();
            if (hasNamespacesFeature()) {
                for (int i = 0; i < this.reader.getNamespaceCount(); i++) {
                    startPrefixMapping(this.reader.getNamespacePrefix(i), this.reader.getNamespaceURI(i));
                }
                for (int i = 0; i < this.reader.getAttributeCount(); i++) {
                    String prefix = this.reader.getAttributePrefix(i);
                    String namespace = this.reader.getAttributeNamespace(i);
                    if (StringUtils.hasLength(namespace)) {
                        startPrefixMapping(prefix, namespace);
                    }
                }
                getContentHandler().startElement(qName.getNamespaceURI(), qName.getLocalPart(),
                        toQualifiedName(qName), getAttributes());
            } else {
                getContentHandler().startElement("", "", toQualifiedName(qName), getAttributes());
            }
        }
    }

    private void handleEndElement() throws SAXException {
        if (getContentHandler() != null) {
            QName qName = this.reader.getName();
            if (hasNamespacesFeature()) {
                getContentHandler().endElement(qName.getNamespaceURI(), qName.getLocalPart(), toQualifiedName(qName));
                for (int i = 0; i < this.reader.getNamespaceCount(); i++) {
                    String prefix = this.reader.getNamespacePrefix(i);
                    if (prefix == null) {
                        prefix = "";
                    }
                    endPrefixMapping(prefix);
                }
            } else {
                getContentHandler().endElement("", "", toQualifiedName(qName));
            }
        }
    }

    private void handleCharacters() throws SAXException {
        if (XMLStreamConstants.CDATA == this.reader.getEventType() && getLexicalHandler() != null) {
            getLexicalHandler().startCDATA();
        }
        if (getContentHandler() != null) {
            getContentHandler().characters(this.reader.getTextCharacters(),
                    this.reader.getTextStart(), this.reader.getTextLength());
        }
        if (XMLStreamConstants.CDATA == this.reader.getEventType() && getLexicalHandler() != null) {
            getLexicalHandler().endCDATA();
        }
    }

    private void handleComment() throws SAXException {
        if (getLexicalHandler() != null) {
            getLexicalHandler().comment(this.reader.getTextCharacters(),
                    this.reader.getTextStart(), this.reader.getTextLength());
        }
    }

    private void handleDtd() throws SAXException {
        if (getLexicalHandler() != null) {
            javax.xml.stream.Location location = this.reader.getLocation();
            getLexicalHandler().startDTD(null, location.getPublicId(), location.getSystemId());
        }
        if (getLexicalHandler() != null) {
            getLexicalHandler().endDTD();
        }
    }

    private void handleEntityReference() throws SAXException {
        if (getLexicalHandler() != null) {
            getLexicalHandler().startEntity(this.reader.getLocalName());
        }
        if (getLexicalHandler() != null) {
            getLexicalHandler().endEntity(this.reader.getLocalName());
        }
    }

    private void handleEndDocument() throws SAXException {
        if (getContentHandler() != null) {
            getContentHandler().endDocument();
        }
    }

    private void handleProcessingInstruction() throws SAXException {
        if (getContentHandler() != null) {
            getContentHandler().processingInstruction(this.reader.getPITarget(), this.reader.getPIData());
        }
    }

    private Attributes getAttributes() {
        AttributesImpl attributes = new AttributesImpl();
        for (int i = 0; i < this.reader.getAttributeCount(); i++) {
            String namespace = this.reader.getAttributeNamespace(i);
            if (namespace == null || !hasNamespacesFeature()) {
                namespace = "";
            }
            String type = this.reader.getAttributeType(i);
            if (type == null) {
                type = "CDATA";
            }
            attributes.addAttribute(namespace, this.reader.getAttributeLocalName(i),
                    toQualifiedName(this.reader.getAttributeName(i)), type, this.reader.getAttributeValue(i));
        }
        if (hasNamespacePrefixesFeature()) {
            for (int i = 0; i < this.reader.getNamespaceCount(); i++) {
                String prefix = this.reader.getNamespacePrefix(i);
                String namespaceUri = this.reader.getNamespaceURI(i);
                String qName;
                if (StringUtils.hasLength(prefix)) {
                    qName = "xmlns:" + prefix;
                } else {
                    qName = "xmlns";
                }
                attributes.addAttribute("", "", qName, "CDATA", namespaceUri);
            }
        }

        return attributes;
    }

}
